The present invention relates to an electrophotographic copying apparatus, and more particularly to electrophotographic copying apparatus using one-component developer particles.
Most of the conventional electrophotographic copying apparatuses have employed two-component developer composition composed of toner particles and carriers. There has recently been developed electrophotographic copying apparatuses using one-component developer particles, or one-component high resistance magnetic toner. This one-component type of the electrophotographic copying apparatus has some problems to be solved, however. When the two-component type electrophotographic copying apparatus copies a document with a high density ratio of the picture information, such as characters, numerals and graphics, to background, it provides a clean copy with little fog, like the copy obtained by the two-component type copying apparatus. But, when it copies documents at a low density ratio, e.g. diazo copied document and low density color document containing red, blue and yellow as fundamental colors, a quality of a copy image is insufficient because the copy image suffers from blurs and poor contrast. When copying a document with a wide density distribution and particularly requiring a good graduation, such as black and white or color photographs, the picture obtained has remarkably poor graduation and may not exactly reproduce of the document image information.